Techniques for sentence transformation and consistency
Strictly speaking, this is impossible. Changing the form of a sentence also changes its meaning. Even active-passive can be important, as you would use it to emphasise what is important: was it relevant what the cat was doing, or was it more relevant what happened to the mouse? True, the purely propositional meaning is not affected by this, but that is only one component of a sentence's meaning.

There has been a lot of work in traditional linguistics about sentence form. You could look at one of the seminal works, Syntactic Structures by Noam Chomsky, where he introduces the concept which later lead to transformational grammar. This influenced a lot of subsequent linguistic approaches, but as far as I am aware transformations are not really that much in the linguistic focus anymore.

For your second question, stylistic consistency, you could look at the work of Douglas Biber. His book Variation across speech and writing introduces a number of (easily extractable) linguistic features that you could use to quantify consistency.